A low but resistant rate of facial abscesses occurring in the NIH nude mouse colony (barrier maintained) has been studied. Staphylococcus aureus has been identified as the causative organism. The dominant phage type is 42E with several isolates also being lysed by phages 44A and 54. Fecal carriage and abscesses were observed in 12 strains of nude mice and the fecal carriage rate is near 100 percent. However, many nude mice are retired as breeders after 9-12 months. Fecal carriage of the same S. Aureus phage types occurs in non-nude cagemates but abscesses have not been seen. Nasal carriage of the causative S. aureus has not been identified in people working with the nude mice. The pathogenesis of this infection is being studied.